Disc drives are well known in the industry. Such drives use rigid discs, which are coated with a magnetizable medium for storage of digital information in a plurality of circular, concentric data tracks. The discs are mounted on a spindle motor, which causes the discs to spin and the surfaces of the discs to pass under respective hydrodynamic (e.g., air) bearing disc head sliders. The sliders carry transducers, which write information to and read information from the disc surfaces.
An actuator mechanism moves the sliders from track-to-track across the surfaces of the discs under control of electronic circuitry. The actuator mechanism includes a track accessing: arm and a suspension. The suspension includes a load beam and a gimbal. The load beam provides a pre-load force to the slider, which forces the slider toward the disc surface. The gimbal is positioned between the slider and the load beam, or is integrated in the load beam, to provide a resilient connection that allows the slider to pitch and roll while following the topography of the disc.
The slider has bearing surfaces which face the disc surface. As the disc rotates, the disc drags air under the slider and along the bearing surfaces in a direction that is approximately parallel to the tangential velocity of the disc. As the air passes beneath the bearing surface, air compression along the airflow path causes the air pressure between the disc and the bearing surfaces to increase, which creates a hydrodynamic lifting force that counteracts the pre-load force and causes the slider to lift and “fly” above or in close proximity to the disc surface.
Typical sliders include a pair of raised side rails that include some of the bearing surfaces and a sub-ambient pressure cavity. As air is dragged under the slider, the bearing surfaces of the raised side rails produce positive pressure gradients relative to the top surface of the slider, which counteract the pre-load force on the slider. Additionally, air dragged under the slider is expanded in the sub-ambient pressure cavity. The expanded air in the cavity provides a self-loading force which forces the slider toward the disc surface. The counteraction between positive pressure gradients developed along the side rails and the pre-load force provided by the suspension generates an air bearing with a high vertical stiffness. When the slider reaches a steady state condition, the slider flies above the disc surface at a desired orientation relative to the disc surface such that reading and writing operations can commence.
Sliders are designed for use with both Contact Start/Stop (CSS) and ramp load or ramp load/unload disc drives. CSS disc drives operate with the slider in contact with the disc surface during start and stop operations when there is insufficient disc rotational speed to maintain the bearing that is necessary to support the slider above the disc. CSS disc drives typically provide a dedicated landing zone near the inner diameter of the disc where no data is written.
In ramp load disc drives, it is unnecessary to land the slider on the disc surface or start the slider in contact with the disc surface. Thus, one advantage to ramp load is that the dedicated landing zone can be eliminated, which increases the data storage capacity of the disc drive. Ramp load disc drives utilize a ramp that is generally adapted to hold the slider by the suspension and is typically located adjacent the outer diameter of the disc. Ramp load disc drives load the slider from the ramp above the disc surface as it rotates, which allows for the immediate formation of the bearing that supports the slider above the disc. Additionally, prior to shutting the disc drive down, the slider is unloaded from above the disc to the ramp.
During these loading and unloading operations, the bearing under the slider can be unstable. This instability can cause excessive slider pitch and roll modulation, which can cause the slider to contact the disc surface. Such contact is undesirable due to the possibility of damaging the disc surface and/or the slider, which could result in data loss and disc drive failure. Additionally, read and write operations are delayed by the unstable bearing under the slider, since they can only be reliably performed when the slider reaches a steady state flying condition.
There is a continued need for improved slider designs for disc drives. More particularly, there is a need for a slider that has reduced pitching and rolling and faster bearing stabilization during ramp load and unload operations.